moisture problems in the wall cavity, year after year.
Moisture induced damage in walls has become a serious issue, and
the subject of many government studies. It has been found that
humid air from the inside of a home, in cold weather, can penetrate
an exterior wall cavity, year after year, and cause rot and even
structural damage. Fiberboard sheathing breathes and lets the
moisture out of the wall cavity to minimize the risk of damage.
Water vapor permeability is important.
The degree to which a material allows water vapor flow-through
is called permeability. Vapor barrier materials, such as polyethylene
film, have low permeability (less than 1 perm) and are installed
to control moisture migration from inside the house, into the
wall cavity. Some popular sheathing materials have such low permeability
that they act like vapor barriers. Bildrite fiberboard sheathing
has an average permeability of 28 perms. It really breathes. Fiberboard
is up to 10 times as permeable as other popular sheathings.
Fiberboard minimizes the risk of moisture damage.
The rate at which water vapor can escape outwards from a wall
cavity is crucial to the safety of the wall and is a function
of the permeability of the wall assembly, particularly the sheathing.
Government studies have found that the use of wet framing lumber,
and exterior sheathing with a very low permeability, may cause
serious moisture problems in the wall. The longer the wall cavity
remains at high moisture content, or damp, the more likely that
rot can gain a foothold. Highly permeable sheathing systems, such
as fiberboard, allow walls to dry more quickly than less permeable
systems and reduce the potential for decay.